Assessing GHG Reduction Opportunities

Almost three years ago, the Technical Working Group on Agricultural Greenhouse Gases (T-AGG) began compiling scientific data and analyzing the most promising agricultural practices for reducing greenhouse gas emissions and sequestering carbon.

Their primary aim is to provide guidance for the development of carbon market protocols, though their work has relevance to other efforts to incentivize shifts in agriculture towards lower carbon footprints, such as the USDA farm bill conservation programs and the investment of cap-and-trade allowance revenue in agriculture that CalCAN is seeking.

The findings are illustrative. Many of the practices with the greatest confidence level and possibility of reducing GHGs are those practiced by the most sustainable producers for years. Here are the top 11 most promising practices (from a summary table on page 31 of the report):

Switch to no-till

Switch to other conservation tillage

Eliminate summer fallow

Use winter cover crops

Diversify annual crop rotations

Incorporate perennials into crop rotations

Switch to short-rotation woody crops

Convert cropland to pasture

Set aside cropland or plant herbaceous buffers

Reduce fertilizer N application rate by 15%

Adjust rice water management to reduce methane emissions

The authors make specific mention of rotational grazing on rangeland. They state “While the C sequestration potential from this practice seems positive, its broader impact on the efficiency of livestock production and the potential for broader mitigation effects is even more promising.”

To their credit, the researchers note that there are often efficiency gains and economic benefits for producers in adopting many of the most powerful GHG-reducing practices. They also attempt to qualify the environmental co-benefits of the practices they evaluated, and on page 39 provide a table summarizing the overlap of multiple ecological benefits for some of the practices.

There are some significant limits to the T-AGG report in terms of applicability to sustainable agriculture in California. First, the authors acknowledge that because most of the available research addresses only the major commodity crops and grazing lands, there is little information available for California’s 350+ specialty crops. They also speculate that there may be little incentive for specialty crop producers to participate in offset credit sales because the payments are likely to be small compared to the relatively high farmgate value of these crops.

Second, each of the farming practices were evaluated in isolation and their additive effects are unknown in most cases — another limitation of the available science. Third, the researchers made a decision not to include research on organic systems, even while stating that the research shows they have great potential for carbon sequestration. In their words:

“Organic agriculture is not addressed as a specific activity in this overview because it incorporates many practices that vary significantly across farms. Research comparing organic and conventional systems has found significantly greater soil organic carbon (SOC) accumulation in the organic systems, both in the United States (Clark et al. 1998; Lockeretz et al. 1981; Pimentel et al. 2005) and abroad (Freibauer et al. 2004). In these systems, C sequestration is enhanced through field application of manure and compost, planting of winter cover crops, high crop-rotation intensity, and maintenance of forested areas for ecological diversity. Many of these practices typical of organic production are assessed individually in this report.”

By omitting an evaluation of organic systems, we believe they and other protocol developers are missing a significant opportunity to assess the cumulative and additive potential for multiple, integrated farming practices to reduce GHG emissions.

Nonetheless, this report provides us with the most comprehensive review to date of the scientific literature available to assess the potential for achieving agricultural mitigation of climate change and to guide public and private investment decisions.